Sugar mill feeding



United States Patent [72] inventor John R. Miller Edgeworth David Ave., Wahroonga New South Wales, Australia [21] Appl. No. 753,835 [22] Filed Aug. 5, 1968 Continuation of Ser. No. 532,736, March 8, 1966, abandoned. [45] Patented Oct. 27, 1970 [32] Priority March 9, 1965 [33] Australia [31] No. 56070/65 [54] SUGAR MILL FEEDING 8 Claims, 1 Drawing Fig.

[521 (LS. Cl 100/43, 100/173,100/176; 146/120z241/35z222/55. 222/56 [51] Int. Cl 3311b 15/2 Bo2c4/0O; AOld 55/00 [50] Field of Search 241/222, 227, 34, 35; 146/116.1, 120, 251; 222/55, 56; 100/43, 45, 173, 176

[56] References Cited UNlTED STATES PATENTS 387,438 8/1888 Parker 146/120 545,286 8/1895 Gutenkunst 146/120X 813,300 2/1906 Hyatt 146/118 Primary ExaminerW. Graydon Abercrombie Attorney-Burgess, Dinklage and Sprung ABSTRACT: Apparatus comprising a pair of toothed feeder rollers for substantially positively feeding fibrous plant materia1, say sugar cane, to a multiroller crushing mill via a pressure chute; said pressure chute being a closed chute inclined to the vertical and flaring slightly in the downward direction towards the multiroller mill. The provision of feeder rollers with teeth for impelling the cane represents an advance over the previously known apparatus of this type in which grooved feeder rollers were provided for frictionally driving the cane. The consequence of the invention is that the principal component of pressure developed in the chute lies in the direction of travel of plant material instead of transversely thereto. Related consequences are that choking of the chute can be eliminated, higher crushing rates are possible, and the power consumption of the crushing mill can be controlled much more uniformly.

Patented Oct; 27, 1970 Y K k L a k M A n n w v vM R EV SUGAR MILL FEEDING This application is a continuation of Ser. No. 532,736, filed March 8, 1966, now abandoned.

This invention has been devised to provide an improved apparatus for, and method of, substantially positively feeding sugar cane or bagasse to a three-roller crushing mill. The invention is described hereinafter in relation to the feeding of this type of material to such a mill, but it will be understood that the described apparatus and method are also adapted for the substantially positive feeding of any fibrous plant material to any multiroller mill.

The more successful feeding techniques previously described have been predicated on the desirability of positive control, but have attempted to achieve this by employing essentially frictional driving means. Thus, according to Australian Pat. No. [07,721, such means comprise a pair of rotatable feeder rollers characterized in that they are adapted to assist cane or bagasse frictionally through their nip to a pressure chute and thence to the intake of a crushing mill. The term chute as used herein means a closed chute inclined to the vertical and flaring slightly in the downward direction. The surfaces of the feeder rollers employed hitherto have been grooved or slotted for more efficient gripping of the cane or bagasse.

This known kind of frictional feeding depends on the development of adequate transverse pressure on the feed as it passes between the roller surfaces. A high crushing ratio (i.e., a high ratio of uncompressed feed blanket depth to separation between feeder roller surfaces) is therefore a prerequisite for substantially positive feeding by this method.

Disadvantages attending such transverse compression of feed are considerable. Thus, feed which has been compressed strongly in a transverse direction is not adapted for even distribution subsequently in the pressure chutepThe compressed cane or bagasse expands on issuing from the feeder rollers and presses against the top and bottom walls of the chute. If the friction developed between the expanded feed and chute walls becomes too high, resistance to feed movement downwardly through the chute becomes excessive; the rollers then slip on the incoming feed and the chute is choked. This problem is particularly serious at high feeding rates.

We have now found that these disadvantages can be overcome by replacing the described essentially frictional driving means by a pair of rotatable feeder rollers characterized in that their surfaces are each provided with a set of spaced teeth of dimensions suitable to impel the feed substantially positively through the pressure chute to the mill, each said tooth having a leading face, a trailing face and two substantially flat side faces, said leading face being curved away from the direction of roller rotation at that site, and the separation between said leading face and said trailing face decreasing upwardly from the roller surface.

It will be appreciated that it is essential to maintain the feeder roller surfaces in a clean condition, and for this purpose, two scraper plates are positioned respectively on opposing walls of the pressure chute and are profiled to register with the teeth of the rollers whereby, as a result of the rotation of these rollers, said surfaces are continuously scraped clean.

The shape of the leading face of each tooth is determined by the requirement that the teeth should be readily retractable from the feed in the chute when passing through the scraper plates.

In a preferred embodiment, the separation between the feeder rollers is such that the arcs described by the set of teeth on one roller overlap the arcs described by the set of teeth on the other roller.

When using the toothed feeder rollers of the invention, substantially positive drive is effected in a simple manner and is essentially independent of transverse compression at the nip. The crushing ratio is small and the principal pressure in the chute therefore occurs in the direction of travel of the feed. As a result, the feed is packed uniformly in the chute and choking does not occur, even at high feeding rates.

An additional advantage flowing from the substantially positive character of feeding achieved by the invention, is that cane or bagasse can be packed into the pressure chute at a greater bulk density than was hitherto possible. This has the consequence that higher crushing rates are possible for a given crushing mill roller speed.

The substantially positive character of feeding achieved by the invention also enables the handling of different types of material. Thus, whole cane pieces, knifed cane pieces, shredded cane or bagasse are impelled towards the crushing mill with the same facility (variable water content notwithstanding). By contrast, grooved rollers cannot grip whole cane pieces, and allow a much greater degree of slip in the handling of knifed or shredded cane and bagasse.

As explained more fully below, a still further advantage of the invention is that the power consumption of the crushing mill can be controlled much more uniformly when the feeder rollers are toothed than when they are grooved. The more precise control of mill power consumption enabled by the use of toothed feeder rollers enables the crushing mill to work more closely to the limit of installed power. This greater use of available power results in more work being done in the crushing mill on each quantity of cane or bagasse so that a greatei' percentage of sucrose is extracted therefrom.

The fibre content of plant materials is highly variable. ln the case of sugar cane, the fibre content changes from variety to variety, and is not uniform even in a single batch of cane of a single variety. Consequently, equal amounts of feed may be expected to involve unequal power consumption when crushed in the mill, high power consumption being required for feed of high fibre content and vice versa. It follows that a crushing mill operating at a given speed can be loaded continuously to an optimum extent only if control means are provided for varying the feed rate to suite the fibre content of the material. Ideally, the feed rate should be corrected before a variant feed reaches the crushing rollers.

In conventional feeder systems. there is no control mechanism for varying feed rate to suite fibre content. Consequently the mill must be set to handle most efficiently feed of highest fibre content. In this situation, the introduction of feed having lower fibre content results in the mill being under loaded;power consumption per ton of fibre falls and juice extraction is reduced. This effect is more evident in the case of a mill having fixed crushing rollers than in the case where some hydraulic loading is provided.

It has now been found that feeder systems incorporating toothed feeder rollers are adapted particularly well for sensitive control of feed rate, fluctuations in mill power with variations in fibre content thereby being reduced to a noticeable extent.

Two alternative types of feed rate control are envisaged: type A, based on the occurrence of feed rate variations in response to variations in the rotational speed of the toothed feeder rollers (possible only when these rollers are driven by an independent variable speed controlled torque drive); type B, based on the occurrence of feed rate variations in response to variations in the availability of feed for transmission through the toothed feeder rollers.

In both cases, the desired feed rate is achieved by a com:. bination of primary and secondary control means. Primary control is exercised with reference to mill power consumption, feed rate being increased to a determined extent as mill power consumption falls, and vice versa. Secondary control is based on a secondary reference point selected so that feed rate can be adjusted to a determined further extent before a variant feed reaches the mill. 7

Preferred embodiments of the described types of feed rate control are discussed hereunder.

TYPE A When toothed feeder rollers are driven by an independent variable speed controlled torque drive, primary control can be achieved by increasing or decreasing to a determined extent the rotational speed of the feeder rollers as mill power consumption respectively falls or rises.

in this system, it has been observed that-for a particular torque setting-an increase in the fibre content of the feed causes a decrease in feeder roller speed; conversely, a decrease in the fibre content causes an increase in feeder roller speed. Some degree of secondary feed control is thereby automatically achieved when ever such a system is employed, but the extent of this secondary control has proved to be inadequate to avoid overloading or underloading the mill.

It has been found that a successful secondary control can be applied by i enforcing a determined further reduction in feeder roller speed whenever the speed is naturally reduced by an increase in the fibre content of the feed, and by ii enforcing a determined further increase in feeder roller speed whenever the speed is naturally increased by a decrease in the fibre content of the feed. The extent in practice to which the feeder roller speed must be further reduced or increased is readily determined by experiment and suitable instrumentation can be devised for automatically carrying out secondary control according to this method.

Variations in feeder roller speed which result from variations in fibre content of the feed can also be shown to occur somewhat in a feeder system employing conventional grooved rollers driven by an independent variable speed controlled torque drive. However, owing to the less positive character of feeding according to this latter system, such variations are not meaningful in practice and cannot be adopted as a basis for successful control.

TYPE B Feed is introduced to the feeder system ofa multiroller mill from a feeder chute, and it will be understood that the orientation of this feeder chute (with respect to the gap between the feeder rollers) determines the availability of feed for transmission through the pressure chute to the mill. Thus, a maximum amount of feed is available for transmission when the outlet of the feeder chute registers completely with the gap between the feeder rollers, and the availability of feed is lessened as the degree of registration is reduced, for example by swinging the feeder chute somewhat across the feeder rollers.

When toothed feeder rollers are driven from the mill prime mover at a speed which bears a constant ratio to the speed of rotation of the mill rollers, it has been found that primary feed rate control can be achieved by increasing or decreasing to a determined extent the registration of the feeder chute outlet with the gap between the feeder rollers whenever the mill power consumption respectively falls or rises.

The substantially positive character of feeding enabled by the use of toothed feeder rollers results in the principal component of pressure in the pressure chute being in the direction of travel of the feed. In addition, there is a minor component of pressure at right angles to the direction of travel of the feed, and this minor component is a fairly sensitive function of the fibre content of the feed passing through the pressure chute. Accordingly, by inserting a pressure-responsive element in the pressure chute and providing suitable ancillary instrumentation, a successful secondary feed rate control can be achieved by increasing or decreasing to a determined further extent the registration of the feeder chute outlet with the gap between the feeder rollers as the transverse pressure in the pressure chute (registered by the pressure-responsive element) respectively falls or rises in response to variations in the fibre content of the feed passing therethrough.

The drawing is a perspective view of apparatus according to this latter embodiment of the invention for transmitting sugar cane or bagasse to a three-roller crushing mill.

The FIG. shows a feeder chute l for supplying cane or bagasse to the feeding system of a sugar mill 2. The feeding system comprises a pair of identical feeder rollers 3,4 and a pressure chute 5 leading to the mill. The pressure chute includes a pressure responsive element 6 in its upper wall. The feeder rollers are driven in the indicated direction from the prime mover of the mill, and their surfaces are equipped with sets of uniformly spaced, identical teeth shaped as hereinbefore defined. In the region of the nip, the arcs described by the teeth on one roller overlap the arcs described by the teeth on the other roller. Suitably, the separation between the feeder rollers is of the order of 7 inches and the height of each tooth above the roller surface is of the order of 4 inches. A pair of scraper plates 7, profiled to register with the teeth of the feeder rollers, are provided in opposing walls of the pressure V chute.

The feeder chute is pivoted at a point 8 and means 9,10,ll,12,l3 are provided for causing it to swing across the gap between the feeder rollers-say, from a first position X to a second position Y whereby to decrease the availability of feed to a determined extent whenever the mill power consumption rises and to decrease the availability of feed to a determined further extent whenever the transverse pressure (registered by the pressure responsive element) rises in the pressure chute.

The means provided for adjusting the orientation of the feeder chute comprise a computer 11 for receiving two signalsa power consumption signal from the mill along path 9 and a pressure signal from the pressure-responsive element along path l0and for transmitting a compound signal along path 12 to a power-operated piston 13 in operative relationship with the feeder chute.

This latter type of control cannot be used successfully in the case of a conventional feeder system employing grooved feeder rollers driven from the mill prime mover at a speed which bears a constant ratio to the speed of rotation of the mill rollers. In such a case, when the availability of feed is lessened by swinging the feeder chute towards the top feeder roller, the feed blanket is compressed between this roller and the opposing wall of the feeder chute and-under these circumstances- -friction between the feed blanket and this wall can develop to such an extent that downward feeding may cease altogether. Additionally, a pressure element as described could not be employed as a satisfactory reference point in a grooved feeder roller system, it having been found in practice that, in such a system, transverse pressure in the pressure chute is not a sensitive function of feed fibre content and that significant pressures are associated only with the occurrence of chokes".

The described primary and secondary control systems also form part of the present invention.

1 claim:

1. Apparatus for substantially positively feeding fibrous plant material to a multiroller mill, comprising: a feeder chute, a pair of rotatable feeder rollers having a gap therebetween and a pressure chute comprising a closed chute inclined to the vertical and flaring slightly in the downward direction, and discharging into the intake of said multiroller mill; said gap between said feeder rollers registering on one side with the outlet of said feeder chute and registering on the other side with the mouth of said pressure chute; the surface of each feeder roller being provided with a set of spaced teeth of dimensions suitable to impel said fibrous plant material substantially positively through said pressure chute to said multiroller mill, each said tooth having a leading face, a trailing face and two substantially flat side faces, said leading face being curved away from the direction of roller rotation and the separation between said leading face and said trailing face decreasing upwardly from the roller surface; the arrangement being such that the crushing ratio is small and the principle pressure in said chute occurs in the direction of travel of said plant material; said apparatus additionally comprising two scraper plates positioned respectively on opposing walls of said pressure chute and profiled to register with the teeth of said feeder rollers and adapted in conjunction with the rotation of said feeder rollers to continuously scrape clean said surfaces in the interstices between said teeth.

2. Apparatus according to claim 1, wherein said gap is such that the arcs described by the ends of one set of teeth overlap the arcs described by the ends of the other set of teeth.

3. Apparatus for feeding fibrous plant material to a mu]- tiroller mill, and for varying the feed rate in response to the power consumption of said multiroller mill, comprising: a feeder chute, a pair of gapped rotatable feeder rollers, a closed pressure chute inclined to the vertical, flaring slightly into the downward direction and discharging into the intake of said multiroller mill; the gap between said feeder rollers registering on one side with the outlet of said feeder chute and registering on the other side with the mouth of said pressure chute; and control means inversely responsive to said power consumption and adapted to regulate the throughput of said feeder rollers as a function thereof; the surface of each feeder roller being provided with a set of spaced teeth of dimensions suitable to impel said fibrous plant material substantially positively through said pressure chute to said multiroller mill, each said tooth having a leading face, a trailing face and two substantially flat side faces, said leading face being curved away from the direction of roller rotation and the separation between said leading face and said trailing face decreasing upwardly from the roller surface, the arrangement being such that the crushing ratio is small and the principle pressure in said chute occurs in the direction of travel of said plant material; said apparatus additionally comprising two scraper plates positioned respectively on opposing walls of said pressure chute and profiled to register with the teeth of said feeder rollers and adapted in conjunction with the rotation of said feeder rollers to continuously scrape clean the surfaces of said feeder rollers between the interstices of said teeth.

4. Apparatus according to claim 3 wherein said gap is such that the arcs described by the ends of one set of said teeth overlap the arcs described by the ends of the other set of teeth.

5. The apparatus of claim 3 wherein feeder rollers are caused to rotate at a speed which bears a constant ratio to the speed of rotation of the rollers of said multiroller mill and wherein the transverse position of the discharge end of said feeder chute with respect to said gap can be varied and wherein said control means includes means for positioning said discharge end with respect to said gap to thereby control the amount of said plant material available thereto.

6. The apparatus of claim 3 wherein said pair of feeder rollers are caused to rotate by an independent variable speed controlled torque drive, said apparatus comprising primary feed rate control means for increasing or decreasing to a determined extent the rotational speed of said pair of feeder rollers whenever the power consumption of said multiroller mill respectively falls or rises, and comprising secondary feed rate contr ol means for increasing or decreasing to a determined further extent the rotational speed of said pair of feeder rollers whenever their rotational speed respectively increases or decreases automatically in response to variations in the fibre content of the feed passing therebetween; said primary feed rate control means and said secondary feed rate control means together constituting said control means inversely responsive to said power consumption.

7. Apparatus for substantially positively feeding fibrous plant material to a multiroller mill, comprising: a feeder chute, a pair of rotatable feeder rollers having a gap therebetween, an independent variable speed controlled torque drive therefor, and a pressure chute comprising a closed chute inclined to the vertical and flaring slightly in the downward direction, and discharging into the intake of said multiroller mill; said gap between said feeder rollers registering on one side with the outlet of said feeder chute and registering on the other side with the mouth of said pressure chute; the surface of each feeder roller being provided with a set of spaced teeth of dimensions suitable to impel said fibrous plant material substantially positively through said pressure chute to said multiroller mill, each said tooth having a leading face, a trailing face and two substantially flat side faces, said leading face being curved away from the direction of roller rotation and the separation between said leading face and said trailing face decreasing upwardly from the roller surface; the arrangement being such that the crushing ratio is small and the principle pressure in said chute occurs in the direction of travel of said plant material; said apparatus additionally comprising two scraper plates positioned respectively on opposing walls of said pressure chute and profiled to register with the teeth of said feeder rollers and adapted in conjunction with the rotation of said feeder rollers to continuously scrape clean said surfaces in the interstices between said teeth; primary feed rate control means for increasing or decreasing to a determined extent the rotational speed of said pair of feeder rollers whenever the power consumption of said multiroller mill respectively falls or rises, and a secondary feed rate control means for increasing or decreasing to a determined further extent the rotational speed of said pair of feeder rollers whenever their rotational speed respectively increases or decreases automatically in response to variations in the fibre content of the feed passing therebetween.

8. Apparatus for substantially positively feeding fibrous plant material to a multiroller mill, comprising: a feeder chute; control means for positioning the outlet of said feeder chute; a pair of rotatable feeder rollers having a gap therebetween and rotating at a speed which bears a constant ratio to the speed of rotation of the rollers of said multiroller mill; a pressure chute comprising a closed chute inclined to the vertical and flaring slightly in the downward direction, and discharging into the intake of said multiroller mill; said gap between said feeder rollers registering on one side with the outlet of said feeder chute and registering on the other side with the mouth of said pressure chute; the surfaces of each feeder roller being provided with a set of spaced teeth of dimensions suitable to impel said fibrous plant material substantially positively through said pressure chute to said multiroller mill; each said tooth having a leading face, a trailing face and two substantially flat side faces, said leading face being curved away from the direction of roller rotation and the separation between said leading face and said trailing face decreasing upwardly from the roller surface; the arrangement being such that the crushing ratio is small and the principle pressure in said chute occurs in the direction of travel of said plant material; said apparatus additionally comprising two scraper plates positioned respectively on opposing walls of said pressure chute and profiled to register with the teeth of said feeder rollers and adapted in conjunction with the rotation of said feeder rollers to continuously scrape clean said surfaces in the interstices between said teeth, and said control means comprising, primary feed rate control means for increasing or decreasing to a determined extent the registration of said feeder chute outlet with the gap between said feeder rollers whenever the power consumption of said multiroller mill respectively falls or rises, and secondary feed rate control means for increasing or decreasing to a determined further extent the registration of said gap with the outlet of said feeder chute whenever the registered transverse pressure in said pressure chute respectively falls or rises in response to variations in the fibre content of the feed passing therethrough, a pressure responsive element being incorporated in an appropriate wall of said pressure chute for registering said transverse pressure. 

